In the interest of both safety and efficiency it is recommend that you have your chimney swept by a professional chimney sweep.
Burning Smokeless Fuel
If you are burning smokeless fuel it is recommended that you have your chimney swept at and at least once a year.
Burning Wood or Coal
If you are burning wood or coal it is recommended that you have your chimney swept at and at least twice a year.
First fire of the season
Never light a fire for the first time, or a long period, without having the chimney swept and also checked for any obstacles such as nests etc.